Cumulative enhancement signal processor

ABSTRACT

A cumulative enhancement signal processor for improving the detection of repetitive signals in a noisy background which signals exist during each of a plurality of repetition intervals. Each repetition interval is divided into a plurality of discrete time intervals called bins. The average signal level in each bin is determined and the estimated mean background noise level for each bin is derived by summing and averaging the signal level in a selected number of bins adjoining the bins next to the test bin. The estimated mean background noise level for each bin is subtracted from the average signal level for the associated bin to derive a residual signal which is then stored. This procedure is repeated for a selected number of repetition intervals with the derived residual signals for each bin being added to the previously derived residual signal for that bin. Since the signal level of a bin containing the information pulse is statistically greater than the estimated mean background noise for that bin, the residual signals accumulate to a relatively high signal level as the repetitive information pulses are accumulated over a selected number of repetition intervals. The residual signal in bins not containing the repetitive information signal will not accumulate to a high residual signal over successive repetition intervals since the difference between the estimated mean background noise level for such bins and the average signal level thereof will tend to zero. If the information signal is shifting timewise with respect to the repetition interval, a plurality of the aforementioned signal processors are connected in parallel with the discrete time intervals or bins generated by each processor being shifted with respect to time at varying rates. Thus, a high accumulation signal will occur in only the processor having its bins shifted at the same rate that the information signal is shifting with respect to the repetition interval. The output of the processor having the highest peak accumulated signal is detected and displayed by an output device.

United States Patent Brown et a].

3,693,100 Sept. 19,1972

[ CUMULATIVE ENHANCEMENT SIGNAL PROCESSOR [73] Assignee: PresearchIncorporated, Silver Springs, Md. [22] Filed: April 9, I971 [2l] Appl.No.: 132,890

[52] U.S. Cl ..328/l65, 328/l 5] [51] Int. Cl. ..ll03k 5/18 [58] FieldoiSearch ..328/l5l, I65

[56] References Cited UNITED STATES PATENTS 3,531,802 9/1970 Brown etal. ..328/l5l 3,201,702 8/1965 Hanulec et a] ..328/l 10 2,736,021 2/1956Sunstein ..328/127 Primary Examiner-James W. Lawrence AssistantExaminer-Harold A. Dixon Attomey-Pennie, Edmonds, Morton, Taylor andAdams and John L. Sigalos [5 7 1 ABSTRACT A cumulative enhancementsignal processor for improving the detection of repetitive signals in anoisy background which signals exist during each of a plurality ofrepetition intervals. Each repetition interval is divided into aplurality of discrete time intervals called bins. The average signallevel in each bin is determined and the estimated mean background noiselevel for each bin is derived by summing and averaging the signal levelin a selected number of bins adjoining the bins next to the test bin.The estimated mean background noise level for each bin is subtractedfrom the average signal level for the associated bin to derive aresidual signal which is then stored. This procedure is repeated for aselected number of repetition inter vals with the derived residualsignals for each bin being added to the previously derived residualsignal for that bin. Since the signal level of a bin containing theinformation pulse is statistically greater than the estimated meanbackground noise for that bin, the residual signals accumulate to arelatively high signal level as the repetitive information pulses areaccumulated over a selected number of repetition intervals. The residualsignal in bins not containing the repetitive information signal will notaccumulate to a high residual signal over successive repetitionintervals since the difference between the estimated mean backgroundnoise level for such bins and the average signal level thereof will tendto zero.

If the information signal is shifting timewise with respect to therepetition interval, a plurality of the aforementioned signal processorsare connected in parallel with the discrete time intervals or binsgenerated by each processor being shifted with respect to time atvarying rates. Thus, a high accumulation signal will occur in only theprocessor having its bins shifted at the same rate that the informationsignal is shifting with respect to the repetition interval. The outputof the processor having the highest peak accumulated signal is detectedand displayed by an output evlce ll Claims, 5 Drawing Figures l3 f0 5" EkCfi T lM E PREVIOUS DECA I INCREMENT SUM SIGNAL STORKEIE ACCUMULATIONOR BIN L24 DISPLAY I7 '5 MEAN PRESENT BACKGROUND M DIFFERENCE SlGNAl-NQ'SE ACCUMULATION PATENTEB SEP 19 1912 SHEET 1 BF 3 W50 HG.

AVERAGE OF EACH TIME SUM a ga {B DECAY'NG 33"?1? ACCUMULATION STORAGEDISPLAY 22 1:3 '7 I? MEAN PREs'ENT BACKGROUND D FF SiGNAL NOISEACCUMULATION F/GZ.

SIGNAL LEvEL 2 3 4 s e 7 e 9 IO t INVENTORS BUCK c. BROWN a CHARLESPORTERFIELD ATTORN E Y5 MTENTED 3.693.100

sum 2 OF 3 SIGNAL FIG. 3.

LEVEL I I INVENTORS I BUCK 0. BROWN a CHARLES PORTERFIELD CUMULATIVEENHANCEMENT SIGNAL PROCESSOR BACKGROUND OF THE INVENTION This inventionrelates to a signal processor and more specifically to a signalprocessor for detecting repetitive information signals in a noisybackground.

In the past signal processors for detecting repetitive signals such assonar pulses have been less than adequate since the average backgroundnoise level I from which an information signal is extracted, heretofore, has been difficult if not impossible to ascertain. Thus, in anocean environment both random and systematic noise components havecontributed to the composite background noise level. Systematic noisecomponents can be attributed to, among other things, the ocean waves,ship movement, temperature gradients, etc. Such noise is difficult topredict at any point in time and no known devices that have attempted toextract an information pulse from such a noise background have beenwholly successful.

An example of a prior art signal processor that attempted to derive thetrue mean background noise at each point in time during a repetitioninterval simply summed the background noise at each point in time duringa repetition interval or period. This summation signal was divided bythe period of the interval to give the average background noise for theinterval. However, this method has proved to be inaccurate when thenoise level varied greatly over a repetition interval.

It, therefore, is an object of this invention to provide a method andapparatus for deriving a more accurate estimate of the background noiseat each interval of a multi-interval repetition cycle.

It is another object of this invention to provide an accurate method andapparatus for detecting and enhancing a cyclic information signal in anoisy background.

It is yet another object of this invention to provide an accurate methodand apparatus for detecting and enhancing a cyclic information signal ina noisy background wherein the information signal is shifting withrespect to a repetition interval.

SHORT STATEMENT OF THE INVENTION Accordingly, this invention relates toa method and apparatus for detecting and enhancing repetitiveinformation signals in a noisy background wherein the informationsignals exist during each of a plurality of repetition intervals.

Each repetition interval is divided into a plurality of discrete timeintervals called bins. The estimated average noise level is determinedand subtracted from the average composite signal level in each bin toprovide a residual signal which tends to zero if no information signalis contained in the bins and which is some value other than zero if theinformation signal is contained in the bin. The estimated noise levelfor each bin is derived by determining the average value of thecomposite signals in a selected number of bins to each side of the binsadjoining the bin of interest. The residual signals from each bin arestored and added to the residual signals derived from the correspondingbin in the succeeding repetition intervals. The residual signal for thebin containing the information signal will tend to accumulate and becomemuch greater than the residual signals from the other bins and,accordingly,

the position of the information signal is not only detected but alsoenhanced.

For information signals that are shifting with respect to the repetitioninterval, a plurality of the aforementioned signal processors areconnected in parallel with the discrete time intervals or bins of eachbeing shifted with respect to the repetition interval at varying rates.A high accumulation signal will occur only in the 0 processor having itsbins shifted at the same rate that the information signals is shiftingwith respect to the repetition interval. The output of the processorhaving the highest peak accumulated signal is detected and displayed byan output device.

Other objects. advantages and features of this invention will becomemore fully apparent from the following detailed description, appendedclaims and accompanying drawings in which:

FIG. 1 is a simplified block diagram representing the functionaloperation of the invention;

FIG. 2 is a graphical representation of a signal input to the processorafter having been divided into discrete time intervals or bins;

FIG. 3 shows a graphical representation of three kinds of backgroundnoise signals encountered by the processor of this invention;

FIG. 4 shows a block diagram of the preferred embodiment of thisinvention; and

FIG. 5 shows a block diagram of the processor of this invention when aninformation signal is shifting with respect to a repetition intervalDETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG.1, a signal input 11 is shown which may originate from a pulse radar,pulse-doppler radar or sonar system wherein the received signals arecharacterized as being repetitive and similar. The composite receivedsignal from such systems is also characterized by a desired informationsignal component which exists briefly during the repetition interval,and a noise component which exists for the complete repetition interval;the noise component being comprised of random noise and systematic noisecomponents. The input signal is divided into a plurality of timeincrements or bins and the average value of each of these increments isobtained at element 13. In addition, the average of the signal level ina selected number of bins to each side of the bins adjoining a bin ofinterest is derived in element I5. This derived average signal is theestimate of the mean background noise for the bin of interest. Theaverage background noise level is derived for each bin in a repetitioninterval. This average background signal is subtracted from the signalaverage of the corresponding time bin for each time bin in differencecircuit 17. The difference of the two averages, that is, the average ofthe energy received in each bin minus the average of the noiseassociated with each bin, is then stored in element 16. During thereception of succeeding input signals, the present signal accumulationis transferred to element 18. The accumulation signal in bin 18 isdecayed or decreased over a number of repetition intervals to prevent anunduly large accumulated signal. This signal is then displayed by adisplay device 22.

The accumulation in element 18 becomes the previous signal accumulationas a new signal is fed to the processor and this signal is added bin bybin in element 24 to the new averages of the corresponding new bins atelement 13. Thus, the system of FIG. I is a continuous or cumulativerefinement loop which may be interrupted or recycled at any time byforcing the previous signal accumulation at 18 to zero.

FIG. 2 shows a graphical display of a typical input signal received bythe processor of this invention. The incoming signal is divided intodiscrete time intervals or bins which may have any suitable timeduration. In the preferred embodiment, the processor is used to enhancesonar pulses. Accordingly, the width or time duration of each bin isapproximately equal to the duration of the sonar pulse plus a correctionfor target elongation. Typically for a pulse having a duration between0.5 seconds and I second, the elongation factor will be 0.1 seconds. Ifthe period between sonar pulses or pings is 50 seconds and the length ofa sonar pulse is l second, the number of bins will be approximately 45for a repetition interval.

In the past, the mean background noise level was determined by summingthe average signal level in each bin and then dividing by the period ofthe repetition interval. The method of ascertaining background noise foreach individual bin was prone to error as will be more fully understoodfrom examination of FIGS. 3(a 3(b), and 3(c).

FIG. 3(a) shows the signal level for a portion of a repetition intervalwhen the background noise level is constant with time. For this case byusing the aforementioned method of determining mean background noise,the correct average background noise for each bin is determined.However, the aforementioned method becomes subject to substantial errorif the background noise varies with time as shown in FIGS. 3(b) and3(c). Thus, in FIG. 3(b) the background noise is rising linearly withtime. By determining the average noise level for a repetition interval,the noise level in the fourth bin may be accurate provided it is thecenter bin of the interval. If it is not the center bin, the calculatednoise level will be either higher or lower than the actual backgroundnoise in the bin of interest. By this invention these errors areobviated. The signal in bins l, 2, 6 and 7 are summed and then dividedby (1/41) which is the total time duration of these bins, to derive amean background noise level for the fourth, the bin of interest. This isrepeated for each bin in the repetition interval. It should beunderstood that the third and fifth bins could be included in thederivation of the mean background noise level but in the preferredembodi ment these are not included to insure that a target signal thatis not centered in a bin will not contribute to the estimate of thebackground for the bin in which it occurs. It also should be understoodthat the signal level of more or less than two bins to each side of thebin of interest can be summed to derive the estimated mean backgroundnoise level. However, by referring to FIG. 3(c) it will be apparent whyonly a few bins to each side of the bin of interest should be summed toderive an estimate of background noise for the bin or interest. Thebackground noise in FIG. 3(c) varies nonlinearly with time as shown.Thus, the background noise level is rising sharply for bins l, 2 and 3but levels off for the remaining bins. If a large number of bins to eachside of bin 4, the bin of interest, are summed to derive a meanbackground level, the average noise level will approach the maximumnoise level which is the level shown in bin 7. This error can beminimized by keeping the extremities of the background bins close to thebin of interest, i.e., by including only a few bins in the noisebackground determination and by keeping the spacing between the bin ofinterest and the nearest background bins at a minimum.

Refer now to FIG. 4 which shows a block diagram of the preferredembodiment of the invention. The processor is provided with two inputs.A pulse timer 29 provides a series of short duration time pulses to ringcounter 31 while the signal input to be detected enters at input 33. Thering counter includes a plurality of outputs from which are taken atotal number, e.g., n+1, of time increment or bin signals.Simultaneously, the desired signal plus associated noise is applied to nnumber of sample and hold circuits 35-41. Circuits of this nature arewell-known in the art and are characterized in that the leading edge ofa time increment pulse from the ring counter 31 immediately destroys allinformation which may be stored in the sample and hold unit. Inaddition, each sample and hold unit integrates the input signal for theduration of the pulse it receives from ring counter 31. This integral isthen held by the sample and hold units until another time incrementpulse is received from the ring counter 31. Thus, the input sample andhold circuits 35-41 are each utilized to obtain an integral value of adifferent bin of the input signal, there being n discrete timeincrements or bins.

The output of each of the sample and hold circuits 35-41 aresequentially fed to a scrial parallel shift register 43. Thus, at theend of the first seven timing intervals, the output of the sample andhold unit 35 is in the seventh stage of shift register 43, the output ofsample and hold circuit 37 in the sixth stage, etc. Once each timinginterval the contents of the first,'second, sixth, and seventh stages ofthe shift register are sensed by summing amplifier 45. The gain ofamplifier 45 is( l/41') or the total period of the four binsv The outputof amplifier 45 represents the estimated mean background noise level ofthe bin of interest and is connected to a series of sample and holdcircuits 47-53 each being associated with a corresponding bin of thedetected input signal. Each sample and hold circuit in sequential orderis pulsed by ring counter 31 along lines 46-52 as the background noiseof its associated bin is being calculated by amplifier 45. Thus, sampleand hold circuit 47 is pulsed when the mean background noise level forthe first bin is being calculated. The output of the amplifier is thenstored in that sample and hold circuit. It can be seen that each of thesample and hold circuits 47-53 store the respective mean backgroundnoise level signal for an associated bin of the input signal beingdetected.

At time n+1, each of the sample and hold circuits 4753 are pulsed byring counter 31. The ring counter pulse at time n+1, which is providedon output line 55, is delayed twice by delays 57 and 59 to provideadditional data processing intervals. The first delayed intervalprovided by delay 57 enables the storing of current information whilethe second delay 59 enables the storing of information from the previousdata gathering interval.

The outputs from sample and hold circuits 35-41 are added at the inputs61-67 of operation amplifiers 69-75, respectively. The mean backgroundnoise signal for each bin as provided by the sample and hold circuits47-53 is simultaneously subtracted at inputs 77-83 of operationalamplifiers 69-75, respectively. At the same time, signals from theprevious trace which have already been processed by the amplifiers 69-75are added at amplifier inputs 85-91 of amplifiers 69-75, respectively.As a result, the outputs of the operational amplifiers 69-75 representthe average of the input signal for each time increment minus theestimated mean background noise level for the corresponding timeincrements plus the signals in each time increment which haveaccumulated from prior operations of the amplifiers 69-75. The outputsof these amplifiers are then stored in sample and hold circuits 93-99and represent the results of current processing. The next set of sampleand hold circuits 101-107 are driven by the second delayed n+1 pulsefrom ring counter 31 and are updated to current processing after thedelay provided by delay 59. Thus, the sample and hold circuits 101-107are updated to store the most recent accumulation of signals for eachrespective time increment upon the occurrence of each delayed n+1 pulsefrom ring counter 31, and these sample and hold circuits store theinformation for display and for successive processing by amplifiers69-75, respectively.

One useful data presentation can be obtained by using a standard storageoscilloscope represented as display 109. The processed data present insample and hold circuits 101-107 must be presented sequentially as afunction of time in order to provide a useful display. Appropriatesequencing is obtained by commutating the outputs of sample and holdcircuits 101-107 with gates 111-117, respectively, that are driven byring counter 31. The gate outputs are connected in parallel and arecoupled to the vertical input of display oscilloscope 109. if desired adecay storage circuit could be incorporated with the sample and holdcircuits 101-107 so that the accumulated signals do not becomeexcessively large.

If the repetitious information signal is shifting with respect to therepetition interval as would happen, for example, if a moving ship orsubmarine was being detected by sonar, the aforementioned circuitrywould not enhance the information signal since the information signalwould not remain in the same time interval or bin. Such a shiftinginformation signal can be detected and enhanced by the circuit of FIG. 5which shows a plurality of the processor circuits 119-123 of FIG. 4connected in parallel. However, each processor circuit 1 19-124 ismodified from that shown in FIG. 4.

Thus, referring to FIG. 4, the phantom block 129 is a variable phaseshift circuit that either delays or advances the delivery of timingpulses from timer 29 to ring counter 31. This has the effect of shiftingthe relative position of each bin generated by sample and hold circuits35-41 either forward or backward in time. Thus, if the object beingdetected is approaching the sonar receiver, the timing pulses and hencethe bins are advanced, and if the object being detected is receding fromthe sonar receiver, the timing pulses and hence the bins are delayed.

Since the rate of motion or range rate of the object being detected isusually an unknown, a plurality of processor circuits are combined inparallel with each having its timing pulses and hence its bins shiftingat a different rate. Thus, for example, processor 119 may have its binsbeing shifted so that an information pulse returning from a shipapproaching at 4 knots is accumulated in a signal bin. Processor 121 mayhave its bins being shifted so that an information pulse returning froma ship approaching at 2 knots is accumulated in a single bin. Processor123 will not have its bins shifted at all so that it will accumulatereturn information pulses from stationary targets and finally, processor124 may have its bins being shifted so that the return signal from anobject receding at 2 knots will be accumulated. It should be understoodthat as many processor circuits can be connected in parallel as arenecessary to cover the necessary or anticipated range rates.

Each of the outputs of the processors 119-124 are coupled to a multipleinput comparator 125 which selects the processor having the greatestpeak signal and gates this signal to an output display device 127 suchas an oscilloscope. The processor having the highest accumulated signalin one of its bins will be the processor that is shifting its bins atthe rate that the input information signal is shifting.

Although a specific analog embodiment of the invention has beendescribed in detail, it should be understood that operational variationssuch as the number or placement of the basic time intervals may beproduced by minor modifications to the ring counter 31 or to the inputpulses from timer 29.

It is also necessary to determine and/or control the total number oftraces used to provide each signal accumulation. This function can beaccomplished by periodically manually or automatically resetting theoutput sample and hold circuits 101-107 to zero. it should also beunderstood that the basic functions of addition, subtraction, divisionand data storage required for the signal processing described above maybe performed by digital as well as analog devices. Although digitalcircuitry is inherently reliable and stable, the required accuracy andresolution for the system described is obtainable with digital circuitryonly with significantly increased cost and complexity. It is for thisreason that an analog device is set forth as a preferred embodiment.

Thus, it should be understood that various modifications arecontemplated and may obviously be resorted to by those of ordinary skillin the art without departing from the spirit and scope of the invention,as hereinafter defined by the appended claims.

We claim:

1. A cumulative enchancement signal processor for detecting andenhancing repetitive and similar information signals in a noisybackground wherein the information signal exists for only a short timerelative to complete repetitive interval and wherein the noisebackground exists for the complete repetitive interval, comprising meansfor dividing said input signals into a predetermined number of timeincrements;

means for determining the average signal level in each of said timeintervals;

means for deriving the mean background noise for each time intervalincluding means for summing the average signal level of a small numberof time intervals relative to the total number of time intervals in eachrepetitive interval, said small number of time intervals being proximatethe time interval for which the mean background noise is beingdetermined;

means for averaging said summation signal over the time intervals summedto obtain a derived mean background noise level;

means for subtracting said average signal level for each of said timeintervals from the derived mean background noise of the correspondingtime intervals, said difference signals each being a residual signalofits associated time interval, and

means for accumulating said residual signals of each time interval withthe residual signals derived in the succeeding repetitive intervalswherein the residual signal of the time interval containing theinformation signal will become large compared to other intervals.

2. The processor of claim 1 wherein said means for summing the averagesignal level of a small number of time intervals relative to the totalnumber of time intervals in each repetitive interval comprises means forsumming the time intervals proximate the time intervals adjoining thetime intervals for which the mean background noise is being derived,said adjoining time intervals being unsummed.

3. The processor of claim 2 further comprising means for decaying withtime over a selected number of repetition intervals said accumulatedresidual signals.

4. The processor of claim 3 further comprising means for shifting saidtime intervals with respect to said repetition interval.

5. The processor of claim 4 further comprising means for shifting saidtime intervals with respect to said repetition interval at the same rateas said information signal is shifting with respect to said repetitioninterval.

6. The processor of claim 4 further comprising:

means for combining a plurality of said processors in parallel, each ofsaid processors receiving said repetitive signal, and each of saidprocessors shifting said time intervals at different rates; and

means receiving the accumulated outputs of each of said processors fordetermining which processor provides the highest accumulation signal,said processor with said highest accumulation signal having a rate ofinterval shift approximately equal to the shift of said repetitionsignal with respect to said repetition interval.

7. [n a cumulative enhancement signal processor, a

method of detecting and enhancing repetitive and similar signals in anoisy background wherein the signals exist for only a short timerelative to a complete repetition interval and wherein the noisecomponent exist for the complete repetitive interval, comprising thesteps of dividing said input signals into a predetermined number of timeincrements, determining the average signal level in each of said timeintervals, I I deriving the mean background noise for each time intervalincluding the step of summing the average signal level of a small numberof time intervals relative to the total number of time intervals in eachrepetitive interval, said small number of time intervals being proximatethe time interval for which the mean background noise is being derived,

averaging said summation signal over the time intervals summed to obtaina derived mean background noise level,

subtracting said average signal level of each of said time intervalsfrom the derived mean background noise of the corresponding timeinterval, said difference signals each being a residual signal of itsassociated time interval, and

accumulating said residual signals of each time interval with theresidual signals derived in the succeeding repetitive intervals whereinthe residual signal of the time interval containing the informationsignal will become large compared to other intervals.

8. The method of claim 7 wherein said summing step comprises the step ofsumming only the signal in those time intervals proximate the timeintervals adjoining the time interval for which the mean backgroundnoise is being derived.

9. The method of claim 8 further comprising the step of decaying withtime over a selected number of rcpetitious intervals said accumulatedsignals 10. The method of claim 9 further comprising the step ofshifting said time intervals with respect to said repetition interval atthe same rate as said information signal is shifting with respect tosaid repetition interval.

11. The method of claim 9 further comprising the steps of combining aplurality of said signal processors in parallel,

shifting said time intervals at different rates in each processor,

comparing the outputs of each of said processors,

and

detecting the output having the greatest peak accumulation signal.

1. A cumulative enchancement signal processor for detecting andenhancing repetitive and similar information signals in a noisybackground wherein the information signal exists for only a short timerelative to complete repetitive interval and wherein the noisebackground exists for the complete repetitive interval, comprising meansfor dividing said input signals into a predetermined number of timeincrements; means for determining the average signal level in each ofsaid time intervals; means for deriving the mean background noise foreach time interval including means for summing the average signal levelof a small number of time intervals relative to the total number of timeintervals in each repetitive interval, said small number of timeintervals being proximate the time interval for which the meanbackground noise is being determined; means for averaging said summationsignal over the time intervals summed to obtain a derived meanbackground noise level; means for subtracting said average signal levelfor each of said time intervals from the derived mean background noiseof the corresponding time intervals, said difference signals each beinga residual signal of its associated time interval, and means foraccumulating said residual signals of each time interval with theresidual signals derived in the succeeding repetitive intervals whereinthe residual signal of the time interval containing the informationsignal will become large compared to other intervals.
 2. The processorof claim 1 wherein said means for summing the average signal level of asmall nUmber of time intervals relative to the total number of timeintervals in each repetitive interval comprises means for summing thetime intervals proximate the time intervals adjoining the time intervalsfor which the mean background noise is being derived, said adjoiningtime intervals being unsummed.
 3. The processor of claim 2 furthercomprising means for decaying with time over a selected number ofrepetition intervals said accumulated residual signals.
 4. The processorof claim 3 further comprising means for shifting said time intervalswith respect to said repetition interval.
 5. The processor of claim 4further comprising means for shifting said time intervals with respectto said repetition interval at the same rate as said information signalis shifting with respect to said repetition interval.
 6. The processorof claim 4 further comprising: means for combining a plurality of saidprocessors in parallel, each of said processors receiving saidrepetitive signal, and each of said processors shifting said timeintervals at different rates; and means receiving the accumulatedoutputs of each of said processors for determining which processorprovides the highest accumulation signal, said processor with saidhighest accumulation signal having a rate of interval shiftapproximately equal to the shift of said repetition signal with respectto said repetition interval.
 7. In a cumulative enhancement signalprocessor, a method of detecting and enhancing repetitive and similarsignals in a noisy background wherein the signals exist for only a shorttime relative to a complete repetition interval and wherein the noisecomponent exist for the complete repetitive interval, comprising thesteps of dividing said input signals into a predetermined number of timeincrements, determining the average signal level in each of said timeintervals, deriving the mean background noise for each time intervalincluding the step of summing the average signal level of a small numberof time intervals relative to the total number of time intervals in eachrepetitive interval, said small number of time intervals being proximatethe time interval for which the mean background noise is being derived,averaging said summation signal over the time intervals summed to obtaina derived mean background noise level, subtracting said average signallevel of each of said time intervals from the derived mean backgroundnoise of the corresponding time interval, said difference signals eachbeing a residual signal of its associated time interval, andaccumulating said residual signals of each time interval with theresidual signals derived in the succeeding repetitive intervals whereinthe residual signal of the time interval containing the informationsignal will become large compared to other intervals.
 8. The method ofclaim 7 wherein said summing step comprises the step of summing only thesignal in those time intervals proximate the time intervals adjoiningthe time interval for which the mean background noise is being derived.9. The method of claim 8 further comprising the step of decaying withtime over a selected number of repetitious intervals said accumulatedsignals
 10. The method of claim 9 further comprising the step ofshifting said time intervals with respect to said repetition interval atthe same rate as said information signal is shifting with respect tosaid repetition interval.
 11. The method of claim 9 further comprisingthe steps of combining a plurality of said signal processors inparallel, shifting said time intervals at different rates in eachprocessor, comparing the outputs of each of said processors, anddetecting the output having the greatest peak accumulation signal.